In recent years, services providing applications on the Internet have been spreading rapidly. As one of these kinds of services, there is a game provided on a site such as an SNS (Social Networking Service). In this case, a game system often provides tools including an email, a chat, a bulletin board for communication. A user gets acquainted with other users by using the tools for communication to establish friendships with them. A user who becomes a friend may participate in a game that another user plays to battle a strong enemy jointly.
A conventional game system extracts users who can be candidate friends, and presents the extracted users to a user who requests the presentation of the candidate friends. (see Patent Document 1)